1. Field of the Invention
The present invention relates to MEMS (Micro Electro Mechanical System) devices and a method of manufacturing MEMS device assemblies.
2. Related Art
A MEMS device is a miniature device, which can typically be formed of a combination of mechanical parts and electrical circuits. The components of a MEMS device can, for example, have dimensions ranging from sub-micrometers to a few hundred micrometers. MEMS devices are typically formed on a semiconductor chip. MEMS devices can, for example, be formed using a lithographic apparatus. There are a number of known applications for MEMS devices, for example they can be used as sensors, actuators or process control units.
In certain applications the flatness of a surface, for example an active surface of a MEMS device, can be important. For example, a MEMS device can be an optical MEMS device (e.g., having an active surface that is arranged to reflect light), and as such the flatness of the active surface can affect its optical properties. It will be appreciated that the flatness of a surface is a measure of the extent to that the surface conforms to a single plane (and can, therefore, be considered as a measure of the evenness of a surface). Since MEMS devices can incorporate very small features, it can be appreciated that a surface can be considered unflat in the context of MEMS devices that in other applications can be considered to have a high level of flatness. For example, it can be desirable for the surface of a MEMS device to have a surface with unflatness in the region of a few nanometers (e.g., about 10 nanometers) or a few microradians maximum slope deviation (e.g., about 0.2 microradians). This can, for example, correspond to fractions of a wavelength of light used to illuminate the MEMS device.
Localized variations in the flatness of a surface of a MEMS device can, for example, be the result of variations in the thickness of the MEMS device itself. A MEMS device can be attached to a supporting substrate to provide a MEMS device assembly and, therefore, variation in the flatness of a substrate to that the MEMS device is attached can (additionally or alternatively) result in variations in the flatness of a surface of the MEMS device. In some applications, it can be extremely difficult, or even impossible, to correct flatness errors by means of alignment adjustments or calibration. Accordingly, it can be desirable to provide a MEMS device that, in at least some embodiments, provides an active surface with improved flatness.
Therefore, what is needed is a system and method to obviate or mitigate one or more of the above-noted issues, whether identified herein or elsewhere.